Several different methods of forming a head on a beverage have been proposed, including various means employed when the beverage is dispensed from a keg or similar bulk container into a drinking vessel. Such means, for example, include a device known as a sparkler which disturbs the flow of the liquid such that the gas in the liquid is encouraged to come out of solution. It is not always possible for a bar or similar outlet to store beverages in bulk containers such as kegs, however, primarily due to space and cost constraints. The space needed to store kegs is clearly significant, and the associated dispensing and chilling equipment also involves significant cost for the proprietor. Many establishments therefore concentrate on selling beverages stored in bottles or cans, which are usually kept in display fridges behind the bar. However, this then presents the problem that, when transferring the beverage from a bottle to a glass, conventional methods of head generation employed with keg or barrel delivery systems cannot be employed.
It is known to employ ultrasonic excitation to produce or increase a head on a beverage. The ultrasonic excitation causes cavitation of the liquid which encourages the gas in the liquid to come out of solution. The gas thus forms as tiny bubbles which migrate to the surface of the liquid, forming a head of froth on the surface. The equipment required is relatively straightforward and does not require much space, and therefore is suitable for use in establishments of the type discussed above which stock only bottled or canned beverages and which may have space constraints.
GB-A-1588624 (Arthur Guinness Son & Company) discloses the use of ultrasonic vibration to form a head of froth. The beer is poured manually from a bottle into a glass, the glass is then placed on a platform of an ultrasonic transducer and the ultrasonic vibration is switched on for a time sufficient to produce the desired head.
GB-A-2166715 (Bass plc) also relates to forming a head ultrasonically. In one embodiment, a shallow metal dish with an electromagnetic transducer on its underside is recessed into a bar counter. After a glass of beer has been dispensed, the glass is placed in the dish and the transducer is operated under the control of a timer to generate the ultrasonic vibrations which form the head.
In both the above prior art systems, the use of water to improve the coupling between the ultrasonic platform and the glass is suggested. Even if a glass or drinking vessel is designed to have a flat base, the base will rarely be perfectly planar due to the nature of the material and the way the glass is manufactured. Therefore, if the glass is placed on a dry platform, the vessel will contact the platform only at a few points and an air gap will exist elsewhere between the two. This air gap greatly reduces the efficiency of the transfer of ultrasonic energy to the glass. By providing a water-filled ultrasonic bath, as is suggested in the prior art, water fills the gaps between the glass and platform, and also surrounds at least the lower portion of the glass, thus improving the efficiency of the energy transfer.
There are certain disadvantages with the use of an ultrasonic bath according to the prior art for the production of a head on a beverage contained in a glass or other vessel. Primarily, the system requires human intervention to maintain the water level in the bath at the optimum level. The water level will fall in use, as some will inevitably be removed each time a glass is taken out of the bath, and the ultrasonic energy also causes a small amount of water to evaporate each time the transducer is activated. Clearly, it is undesirable to rely on human intervention (especially busy bar staff) to keep the water level topped up.